This invention relates to the construction of gravel pack or prepack elements in steam injection wells. In particular it relates to the use of granular sintered bauxite material as the packing material for a gravel pack or prepack placed in a steam injection well.
Gravel packs are used in the oil well industry as downhole filters designed to prevent formation sand from entering the wellbore and causing subsequent damage. A gravel pack is placed by pumping a gravel slurry downhole around a liner. Once in place, the gravel prevents formation sand migration while the liner retains the gravel. A prepack is a surface-made gravel pack where gravel is retained within two concentric screens. Both a gravel pack and a prepack can be used in open or cased holes. They have been used successfully for many years as sand control techniques with the gravel pack being the most common and effective method. Typical application of either a gravel pack or prepack is in wells producing fluids from loosely consolidated sandstone. These sands may have little or no cementing material and as a result of fluid flow into a wellbore, the formation material may readily be produced and cause severe wellbore or surface damage due to erosion or plugging.
The usual filter medium in a gravel pack or prepack is silica gravel presized so that its pore structure will prevent passage of formation sand. It is surface mined from unconsolidated sand deposits and then processed by screening to produce a narrow range of particle sizes. The prior art has established primary and secondary size ranges and acceptable range tolerances recommended for gravel packing, particularly when used in petroleum producing wells.
The life of a gravel pack or prepack installed in a wellbore may not be permanent. Some failures are attributed to improper placement of gravel packs or screen erosion in prepacks. Two common threats to a gravel pack or a prepack are plugging and degradation or chemical decomposition of the gravel material within the pack. For many operating conditions such destruction is not a threat because the fluids produced or injected through the pack are not corrosive to the silica gravel. However, a significant application of gravel packing (and to a lesser extent, use of prepacks) is in wells undergoing steam injection. It has been demonstrated that the conditions that exist in steam injection wells are highly conducive to silica gravel dissolution and subsequent sand control failure when the well is later used as a producing well. (See Reed, M. G.; "Gravel Pack and Formation Sandstone Dissolution during Steam Injection," J. Pet. Tech. (June 1980) p. 941; and McCorriston, L. L. et al.; "Study of Reservoir Damage Produced in Heavy Oil Formations Due to Steam Injection," SPE Preprint 10077, SPE Fall Mtg., San Antonio, TX, Oct. 5-7, 1981.)
The liftetime of a gravel pack or prepack in thermal wells could be extended to improved economic levels if the silica gravel could be replaced with a more stream resistant material. A major disadvantage of using silica gravel in thermal wells is its solubility. A replacement for silica gravel would preferably have all the characteristics which are beneficial to sand control while being less soluble in the steam that is to be injected through the pack.